Electronic equipment for business and entertainment has proliferated in recent years. This proliferation has resulted in an increase in the need for small, inexpensive and efficient power supplies. One common type of power supply is a dc-to-dc converter. As will be appreciated by those of skill in the art, this type of converter accepts electrical power at one voltage level, converts it to high frequency alternating current, uses a transformer to adjust the voltage level and isolate the power source from the electronic load, and rectifies the resulting alternating current to direct current. Such converters are simple, low cost means for providing the power required by electronic equipment. The reason that a high frequency alternating current is used as an intermediate step is to reduce the size of the required transformer.
Converters are often used to power portable equipment or to recharge batteries either internally in the equipment or externally. Some dc-to-dc power supplies are powered by standard household current rectified to provide the direct current input. These types of supplies often take the form of plug-mounted structures where the entire power supply is supported by the electrical connector pins on the plug.
In power supplies such as plug-mounted converters, size, weight and cost are several of the important criteria in designing the converter. For example, if the number of components can be reduced, then the size and complexity of the converter can also be reduced. In the past, it has been found that resonant, self-oscillating dc-to-dc converters may meet many of the requirement of such plug-mounted converter applications. One type of converter is a push-pull converter. These types of converters are discussed in more detail in the background of U.S. Pat. No. 5,303,137 issued to Peterson, the specification of which is hereby incorporated herein by reference. One drawback of these prior art converters, however, is that they require either expensive and lossy square loop magnetics or complicated control circuitry. This has the effect of increasing the size and weight of the converters. Moreover, these prior art converters also have poor short circuit and/or open circuit characteristics, requiring expensive and complicated special overload protection control circuitry.
An improvement to these converters is disclosed in U.S. Pat. No. 5,303,137 to Peterson, which was incorporated by reference above. This patent discloses a small, compact dc-to-dc converter using a half-bridge configuration. The frequency-determining circuit of the power supply requires only the inherent magnetizing and leakage inductance of the transformer and no separate conductive elements. However, the circuit operates better when using a regulated circuit in order to properly operate the electronics of the device to which the power supply is attached.
Accordingly, there arises a need to for an improved regulated multi-resonant self-oscillating converter circuit. The present invention directly addresses and overcomes the shortcomings of the prior art.